Procedure for fixing nongelating emulsions and improved nongelatin emulsion fixing baths



Patented Aug. 12, 1947 EMULSIONS AND IMPROVED NONGELATIN EMULSION FIXING BATHS John I. Crabtrec and George T. Eaton, Rochester, N. Y., assigno'rs to Eastman Kodak Company, Rochester, N.-Y.,-a corporation of New Jersey No Drawing. (Application June 23, 1943, Serial No. 491,914

9 Claims.

This invention relates to improved photographic procedure for the treatment of non-gelatin emulsion photographic elements and in particular to improved procedure for fixing such photographic elements. The invention also pertains to improved fixing compositions for such photographic elements. 1

Various non-gelatin materials have been used heretofore as protective colloids or carriers as a substitute for gelatin in photographic silver halide emulsions. Thus, cellulose esters and synthetic resins such as cellulose nitrate, acetate, acetate-butyrate; polyvinyl acetals such as polyvinyl acetaldehyde acetal and polyvinyl butyraldehyde acetal; cold water solubl polyvinyl acetaldehyde acetal, polyvinyl alcohol and polyvinyl esters such as hydrolized polyvinyl acetate have been used for this purpose. These substitutes are superior to gelatin in many respects but it has been noted that they frequently are not satisfactorily permeated by fixing solutions so that the removal of silver halide by conventional fixing solutions has in many cases been incomplete or required an inordinately long period of time.

This invention has for its object to provide improved procedure for the fixing of photographic elements bearing a non-gelatin emulsion. Another object is to provide improved fixing baths which permit rapid fixing of non-gelatin emulsions, and especiall those which have limited permeability to water or to the usual fixing baths. Other objects are to improve the state of the art.

These and other objects are accomplished by our invention which includes immersing a photographic element, which comprises a non-gelatin layer containing a developed silver halide photographic image, in a bath which contains a thiocyanate and thiourea as the essential fixing constituents.

In the following examples and description we have given several of the preferred embodiments of our invention, but it is to be understood that these are set forth for the purpose of illustration and not in limitation thereof.

Examples of thiocyanates which may be used are sodium, potassium and ammonium thiocyanate; organic thiocyanates such as thiocyan catechol may be used, but we prefer to use inorganic thiocyanates.

Sodium thiocyanate-thiourea mixtures are preferably used in aqueous solutions containing between about 6 and 50% thiocyanate to between about .03 and thiourea. On the other hand the thiourea may serve as the major constituent in which case between about 2 and 8% thiourea to between about .1 and .5% thiocyanate is preferably employed. When using amounts in the upper portion of the ranges given for one agent it is preferable to use amounts in the lower portion of the range for the other fixing agent. Fixing baths containing the above-noted proportions of the essential fixing constituents have been tested and in each case have been found to give a fixing time of three to three and one-half minutes or less. The exact proportions and quantities used depend upon the composition of the non-gelatin. carriers which have been produced with sufiicient variation in structure to require fixing baths embodying all of the proportions given above, Proportions somewhat outside the ranges given can be used with satisfactory results if slower fixing times can be tolerated. In general the higher the concentration of both of the essential constituents the shorter will be the fixing time. Proportions in the higher ranges are not ordinarily used except for nongelatin emulsions which are very impermeable. The concentrations indicated give a completely clear film free of silver halide in three to three and one-half minutes. Similar tests with a conventional fixing loath containing 30% hypo required an hour for a similar degree of fixing.

The invention is applicable to non-gelatin emulsions in general and will enable shorter fixing times with all such emulsions, It is of particular value in connection with those non-gelatin emulsions which have limited permeability to water.

What we claim is:

1. The process of rapidly fixing a photographic element which includes a non-gelatin layer selected from the group consisting of cellulose esters and synthetic resins of limited permeability to water containing a developed silver image which process comprises immersing said photographic element in a bath which contains as the essential fixing constituents a Water soluble thiocyanate and thiourea. V

2. The process of rapidly fixing a photographic element which includes a non-gelatin layer selected from the group consisting of cellulose esters and synthetic resins of limited permeability to water containing a developed silver image which process comprises immersing said photographic element in a bath which contains as the essential fixing constituents between 6 and 50% a water soluble thiocyanate and between .03 and 25% thiourea.

3. The process of rapidly fixing a photographic element which includes a non-gelatin layer se- 3 lected from the group consisting of cellulose esters and synthetic resins of limited permeability to water containing a developed silver image which process comprises immersing said photographic element in a bath which containsas the essential fixing constituents between 2.0% and 8.0% thiourea and between .1% and .5% a water essential fixing constituents a water soluble thiocyanate and thiourea.

5. The process of rapidly fixing a photographic element which includes a non-gelatin layer selected from the group consisting of cellulose esters and synthetic resins of limited permeability to water containing a developed silver image and having but limited permeability to water Whichprocess comprises immersing said photographic element in a bath which contains as the essential fixing constituents between 6 and 50% water soluble thiocyanate and between .03 ,and 25% thiourea.

6. The process of rapidly fixing a photographic element which includes a non-gelatin layer selected from the group consisting of cellulose esters and synthetic resins of limited permeability to water containing a developed silver image and having but limited permeability to water which process comprises immersing said photographic element in a bath which contains as the essential fixing constituents between 2.0% and 8.0% thiourea and between .1% and .5% water soluble thiocyanate.

7. A fixing composition adapted to rapidly fix a photographic element which includes a nongelatin layer selected from the group consisting of cellulose esters and synthetic resins of limited permeability to water containing a developed silver image which composition comprises a mixture of a water soluble thiocyanate and thiourea.

'8. A fixing composition adapted to rapidly fix a photographic element which includes a nongelatin layer selected from the group consisting of cellulose esters and synthetic resins of limited permeability to water containing a developed silver image which composition comprises between 6 and 50% water soluble thiocyanate and between .03 and 25% thiourea.

9. A fixing composition adapted to rapidly fix a photographic element which includes a nongelatin layer selected from the group consisting of cellulose esters and synthetic resins of limited permeability to water containing a developed silver image which composition comprises between 2 and 8% thiourea and between 1 and 5% water soluble thiocyanate.

JOHN I. CRABTREE. GEORGE T. EATON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Mees, The Theory of the Photographic Process, The Macmillan Co., New York, 1942, pages 462 and 465 cited 

